To be brief, it is accurate to the extent of not reporting any real fallacies but has a bias in terms of the way Marx frames the events. By this point in time, Marx had already formed the basis of his socioeconomic theory and it is definitely visible within his writing.

Now, assuming that you've haven't read anything already, you must keep in mind that this is a work of live reporting (Marx was writing for a European branch of the New York Tribune). And much like the New York Times on the Malaysian Airline, there are elements of embellishment and flamboyancy incorporated to make this more appealing to the reader and those should not necessarily be a reflection of the character or viewpoint of Marx.

On a similar note, you must keep in mind that all news can and will be politicized with a clear bias, and since Marx was writing for a New York newspaper, there is a clear bias for the Union. However, this is not necessarily a bad thing in this particular case. Marx in fact, only signed on because the New York Tribune was a progressive abolitionist paper which both mirrored and helped shape his own views, you should read for these moments when he makes breakthroughs.

In terms of factual accuracy, Marx will be no more and no less accurate than most other American news sources that were his contemporaries. But keep in mind, that even facts can be skewed. For example, in the 2008 Olympics, China won the most Gold Medals and the US won the most medals overall. Chinese newspapers announced to the world that the US newspapers had reported that America had won because they had the most medals. Similarly, American newspapers announced to the world, that Chinese newspapers announced a Chinese victory on the basis of the most Gold Medals. Interestingly enough, it was just a happy coincidence that Chinese Newspapers always reported by Gold Medal count and that American Newspapers always reported by Total Medal count. The moral of this story is, that even without an intentional bias, facts can be reported differently, and that will definitely appear in Marx's writings.

Now for personal bias. Marx as a writer focuses a little excessively on the concept of slavery and on the concept of an war wrought by economic interests of the south. Now slavery is a personal point of interest of Marx, but it was also something that had long since became taboo in Europe, so which forms his reaction in his articles? Likely both, but up to you. With economics however, it is exceedingly clear that Marx likes to talk about how it was a matter of money and nothing but that caused war to break out and it is quite fun to read for the moments where he gets really passionate about it.

Interestingly enough, Marx left the New York Tribune the moment they adopted a different stance (more middle of the line) and told him to take a neutral stance favoring immediate peace with a retention of both Union and Confederacy.

If there was something I left out, please feel free to ask!

Citations Karl Marx: A Nineteenth-Century Life by Jonathan Sperber Western Civilization since 1789 by Jackson J. Spielvogel

If this is for a class, or especially if this is for personal enjoyment, I would strongly recommend Karl Marx: A Nineteenth-Century Life. It is an excellent book and goes in depth into the influences upon Marx and what lead him to develop his pro-proletarian stance, among which include an universal sentiment of resentment for what a price of progress via Industrial Revolution was payed by the common man.

here's the link http://www.amazon.com/Karl-Marx-A-Nineteenth-Century-Life/dp/0871404672